1. Field of the Invention
The present invention relates to a variable flow control apparatus for an actuator of a heavy construction equipment, and in particular to a variable flow control apparatus for an actuator of a heavy construction equipment that is capable of implementing an efficient operation of an actuator by allowing the hydraulic fluid to flow from a hydraulic pump to an actuator by a constant flow even when the flow control signal pressure applied to a seat valve openably and closably installed in a discharge flow path of a hydraulic pump exceeds a certain pressure level.
2. Description of the Background Art
As shown in FIG. 1, conventional flow control apparatus for an actuator of heavy construction equipment includes a directional control valve 100, a seat valve assembly 500 and a pilot flow control valve 2.
The directional control valve 100 controls a start, stop and direction change of a hydraulic actuator (such as a boom cylinder, etc.) according to the switching operation of a spool 3 when pilot pressure is applied.
The seat valve assembly 500, which is openably and closably installed in downstream flow paths 7A, 7B and the flow path 7C, limits the flow of hydraulic fluid supplied to a pair of main variable throttles 16A and 16B from the hydraulic pump through the flow paths 7A, 7B and 7C and additionally limits the flow of a pair of load paths 6A and 6B.
The pilot flow control valve 2 controls the movement of the seat valve assembly 500 according to the switching operation of a pilot spool 41 when pilot pressure Pi is supplied.
The seat valve assembly 500, which is operated by the pressure difference between a pair of the load paths 6A and 6B and the flow path 7C, includes a first seat valve 501 and a second seat valve 502. The first seat valve 501, which moves in a housing 1, includes a variable throttle 512 for pilot pressure control adapted to vary an opening area with its movement. And the second seat valve 502, which moves relative to the first seat valve 501, has a variable throttle 511 adapted to vary an opening area of the flow path 7C of the hydraulic pump to the flow paths 7A and 7B with its movement.
In the second seat valve 502, the flow path 7C is connected with the flow paths 7A and 7B through the variable throttle 511. The path communicating with the variable throttle 512 is connected with a pilot path 521 of the pilot flow control valve 2. Here, the pilot path 521 is disconnected with a pilot path 522 of the hydraulic pump by the pilot spool 41 that is in the neutral state.
In the drawings, reference numeral 1 represents a housing in which a spool 3 is switched, and a seat valve assembly 500 is installed. The reference numeral 525 represents a variable throttle that is formed in an outer portion of the pilot spool 41 and is varied with the movement of the pilot spool 41. Reference character C represents a spool cap, which is installed one end of the directional control valve 100 and has an elastic member D adapted to elastically force an initial stage in which the hydraulic fluid from the pump path to the load paths 6A and 6B is blocked.
Therefore, in the case that the pilot pressure Pi is not applied to the pilot flow control valve 2, the second seat valve 502 is naturally moved by the pressure difference between the load paths 6A and 6B and the flow path 7C of the hydraulic pump, so that it is possible to disconnect the flow path 7C from the flow paths 7A and 7B without time delay even when the pressure in the load paths 6A and 6B is higher than the pressure of the hydraulic pump, for thereby preventing a dangerous problem that the actuator is not controlled.
In the case that the flow of hydraulic fluid supplied to the actuator should be limited in order to drive a hydraulic motor (not shown) or an actuator with a big load, the pilot spool 41 is switched in the left direction as shown in FIG. 1 in proportion to the pilot pressure Pi applied to the pilot flow control valve 2. With this, the blocked pilot paths 522 and 521 are opened through the variable throttle 525 of the pilot spool 41, and the pressure of the hydraulic fluid of the hydraulic pump passes through the pilot paths 522 and 521 and is applied to a pressure chamber 524 of the first seat valve 501.
Here, since the first seat valve 501 is moved in the downward direction as shown in FIG. 1 so that the opening area of the variable throttle 525 of the pilot spool 41 may be varied in proportion to the opening area of the pilot pressure control variable throttle 512, the second seat valve 502 is limited to move in the upward direction.
With the movement of the second seat valve 502 being limited, the flow of hydraulic fluid from the flow path 7C to the flow paths 7A and 7B of the hydraulic pump can be controlled.
However, in the conventional flow control apparatus, if the pilot pressure Pi applied to the pilot flow control valve 2 exceeds a certain pressure, the first seat valve 501 is moved in the maximum downward direction as shown in FIG. 1, so that the second seat valve 502 is closed.
Therefore, while the hydraulic priority of operations can be implemented by limiting the flow of hydraulic fluid from the flow path 7C to the flow paths 7A and 7B of the hydraulic pump, a pressure loss may occur due to a throttling in the hydraulic fluid paths in the case that the pressure exceeds a certain pressure level during the combined operations.